1. Field of the Invention
The present invention relates to a decurling method and apparatus, and film production method. More particularly, the present invention relates to a decurling method and apparatus in which a multi-layer film to be produced can be free from occurrence of fold creases, and film production method for the multi-layer film.
2. Description Related to the Prior Art
Cellulose acylate film is a polymer film having good performance with transparent and soft property. Various uses of the polymer film are known, including a window laminate, touch panel film, film for an ITO board, membrane switch film, three dimensional decorative film, optical functional film for a flat panel display panel, and the like.
Those uses are classified in two types. In a first type, a surface of the polymer film is touched by a finger, fabric, touch pen or the like. In a second type, the surface of the polymer film is rubbed by a finger, fabric, touch pen or the like. There occurs a problem of possible scratch on the surface of the polymer film. To solve this problem, a hard coat layer is formed on the polymer film with a higher hardness than the polymer film.
An example of method of producing a multi-layer film including the hard coat layer formed on the polymer film. In a first step of coating application or coating step, a surface of the polymer film is coated with a material curable with curing energy such as ultraviolet radiation and an electron beam, to form a layer. Then in a drying step, the layer is dried. In a step of curing or energy application, the curing energy is applied to the layer. The layer becomes the hard coat layer upon application of the curing energy. The multi-layer film is obtained as a product.
Reaction of the polymerization is used for changing the layer into the hard coat layer. There occurs a curl in the multi-layer film in the polymerization in a manner to direct the hard coat layer inwards. Phenomena of curling have been found in various kinds of the multi-layer film including the multi-layer film having the hard coat layer. To decurl the multi-layer film, JP-A 2003-195051 discloses a method of vapor supply step to apply fluid vapor to the multi-layer film, the fluid vapor being one of water vapor or non-water vapor of organic solvent.
For mass production of the multi-layer film, transport rollers are used to transport a support film of a continuous form. Plural devices are arranged on a transport path for the support film, including a coater, a dryer, and a curing energy source in an order in a moving direction. The coater is used for the coating application of the layer. The curing energy source is used for the curing. Also, a vapor source is disposed downstream of the curing energy source for decurling the multi-layer film if a curl has occurred in the multi-layer film. It is possible to produce the multi-layer film in a large scale under the curl control, because the coating application, the curing and the vapor supply step can be consecutive.
In FIGS. 11 and 12, multi-layer film 201 includes a support layer 201b and a hard coat layer 201a. It is likely that fold creases or wrinkles 205 are created on the multi-layer film 201 before or after a task in the vapor source for the vapor supply step. The fold creases 205 protrude from the surface of the multi-layer film 201 and extends in a moving direction A of the multi-layer film 201. A height H of the fold creases 205 in a serious situation may be as large as 1 mm. The multi-layer film 201 cannot be used as a product if the fold creases 205 are present.